Electronic products typically include a circuit board or substrate bearing conductive traces of circuitry of the product. During the prototyping or throughout the course of the manufacturing of an electronic product electrical characteristics of the product are tested to ensure proper design of the product or to monitor the manufacturing processes. This can be accomplished by establishing temporary electrical connections to the circuit traces using a test probe.
For example, line impedance of circuits is of significant interest to designers and manufacturers of electronic products having printed circuit boards (PCBs). Time-domain reflectometry is one technique for measuring line impedance. Various test probes have been developed to temporarily connect test points of the printed circuits of a PCB to instrumentation of a time-domain reflectometer (TDR). These test probes include a signal conductor and associated signal tip for delivering signals to/from the signal test point of the circuit, and a ground conductor and associated ground tip for providing a ground voltage to a ground test point of the circuit.
One class of such test probes employ a coaxial cable or ‘coax’ as the transmission line for temporarily connecting a device under test (DUT) to instrumentation of a TDR. In this case, the signal conductor is provided by the core of the coax and the ground conductor is provided by the shield of the coax. A typical impedance of a test probe comprising a coax is 50 Ohms. There are numerous commercially available probes that employ a 50 Ohm coax. Examples of these test probes include TDR test probe model number P8018 SE made by Tektronix, Inc. of Beaverton, Oreg., Single-Ended RF/TDR test probe made by HSProbe of Santa Clara, Calif. TDR Probe Model Nos. A0113866 and A0137855 made by Inter-Continental Microwave of Chandler, Ariz., and Microwave Z Probe made by Cascade Microtech of Beaverton, Oreg.